For many years, scroll fluid machines have been widely used as compressors for air conditioners. In a typical scroll fluid machine, a fixed scroll is provided with a spiral wrap and a movable scroll is also provided with a spiral wrap, wherein these fixed and movable side spiral wraps engage with each other to form fluid chambers. In this scroll fluid machine, the movable scroll performs orbital movement, in association with which the fluid chambers vary in volume. For example, in a scroll fluid machine which constitutes a compressor, the volume of a fluid chamber placed in the confined state is gradually decreased to thereby compress fluid in the fluid chamber.
In the above-described scroll fluid machine, it is required to restrict rotation of the movable scroll. As a mechanism for restricting rotation of the movable scroll, there is a widely used mechanism such as an Oldham ring mechanism disclosed in JP-A-2004-19545.
More specifically, in a scroll fluid machine employing an Oldham ring mechanism, a movable scroll is placed, through an Oldham ring (Oldham joint), on a housing. The housing is secured in position together with a fixed scroll. Two pairs of keys are formed on the Oldham ring such that they project therefrom. In other words, the Oldham ring is provided with a total of four keys, two of which are engaged into associated key grooves formed in the housing and the remaining two of which are engaged into associated key grooves formed in the movable scroll. And each of the keys of the Oldham ring slides along its associated key groove, whereby rotation of the movable scroll is controlled.